The experiments are designed to first, characterize the contributions of the interposed and dentate nuclei of the cerebellum in the kinematic and dynamic control of reaching. Cats are trained to perform a multijoint task, reaching into a small tube held at varying heights in order to obtain food. This is a rapid, well-characterized movement performed with a high degree of accuracy in an intact cat. In the proposed studies, measures of limb trajectory, electromyographic activity, and joint torques will be made during specific inactivation of the interposed or dentate nuclei in cats as reaching movements are made. Inactivation will be produced with microinjections of the GABA agonist muscimol. The prediction is that inactivation of the nuclei will result in inaccuracies that are the consequence of specific errors in trajectory. The experiments will test the hypothesis that these errors can be attributed to a failure to compensate for interaction torques that develop because multiple limb segments are used to produce the movement. The specific contributions of the interpositus and dentate to adaptive control of limb trajectories will be investigated using a series of five variations of the basic reaching task to challenge the animal's capacity to use either somesthetic or visual information to trigger corrective responses during a movement or to plan subsequent movements. Two tasks, the load and obstacle tasks, depend primarily on the use of somesthetic information. On anatomical and physiological grounds, performance of these tasks should be impaired by inactivation of the interpositus. The dorsal accessory olive projection to the nucleus interpositus and intermediate cerebellum is driven primarily by proprioceptive stimuli. The lateral cerebellum and dentate, however, receive a non-somatotopic olivary input and a major visual input through the pontine nuclei. Thus, the prediction is that tasks that involve non-homotopic information (i.e., the barrier, moving target, and timing tasks) will be impaired by dentate inactivation. In the second series of experiments, the contributions of the parvicellular and magnocellular divisions of the red nucleus to multijoint trajectory control and adaptation will be examined using the same behavioral paradigms. It is hypothesized that part of the behavioral effect of inactivation of the nucleus interpositus will be mediated by the magnocellular red nucleus and the rubrospinal system, since the major input to the magnocellular red nucleus is the interpositus. The effects of parvicellular red nucleus inactivation are expected to be more complex. This nucleus receives dense projections from both the dentate nucleus and the motor cortex and is part of a complex precerebellar circuit and may exert its effects through multiple descending pathways.